PIEZOMODULATED-REFLECTIVITY STUDY OF MINIBANDS IN ALXGA1-XAS GAAS SUPERLATTICES/

We report the observation of miniband formation in superlattices of Al xGa1-xAs/GaAs, grown by molecular beam epitaxy, manifested in their pi ezomodulated-reflectivity spectra when studied as a function of well ( l(w)) and barrier (l(b)) widths. The piezomodulated-reflectivity spect ra reveal signatures of well separated optical transitions both at the Brillouin zone center and at the zone boundary extending to energies above the AlxGa1-xAs barrier. The clarity and sharpness of the spectra l features allow an unambiguous identification of experimental transit ion energies with those calculated using the full eight-band k.p envel ope-function approximation solved with the finite-element method. With l(w) = 25 angstrom [9 monolayers (ML)], l(b) = 20 angstrom (7 ML), an d x = 0.34, the lowest energy transition at the miniband zone center a nd at the corresponding zone boundary are separated by 158 meV. With l (w) = 74 angstrom (26 ML) and l(b) = 45 angstrom (16 ML), the spectra correspond to quantum states in a multiple quantum well. Features asso ciated with monolayer fluctuations in layer thickness are also observe d.